'Radio eyes' capture plasma tubes floating above our heads

Wednesday, June 3, 2015, 11:32 AM - Thanks to the brilliant and creative use of a telescope by an Australian university student, radio astronomy and GPS navigation may have just become easier. Here's how she did it.

High above our heads, from about 60 kilometres up to the edge of space, is a region of our atmosphere that is filled with charged particles - electrons and ionized gases - called the ionosphere. This is the region of the atmosphere where the "harder" radiation from the sun (x-rays and extreme ultraviolet) are absorbed, and where auroras show up due to geomagnetic storms.

It's also a region of great importance to communications, GPS navigation and radio astronomers, due to how it can block, distort and propagate radio waves. Knowing more about how this region of the atmosphere behaves, and how that behaviour influences radio signals, was the sole purpose of the US Military's High-Frequency Active Auroral Research Program (H.A.A.R.P.) installation in Alaska.

It's long been thought that Earth's magnetic field organized the ionized gases (plasma) into long tubular structures that can stretch nearly from pole to pole, however until now there was no way to detect these structures and properly image them.

What is a "Plasma Tube"?

Earth's magnetic field - generated by the planet's core and extending out into space - can be thought of as a series of looping lines, fairly evenly spaced, that stretch from pole to pole, arching high over the surface of the planet. Since the ionized gases (plasma) in the ionosphere are charged, this charge means that they generate an electric field as they move about, and thus they can be influenced by magnetic fields.

In this case, the charged particles "converge" on the field lines, but rather than simply clumping there or flowing along the lines, the plasma particles orbit around them. If you were to look at one of these in cross section, the (in reality, invisible) field line would be in the middle, with a circle of particles zipping around it. Seen in three dimensions, the multitude of particles in the ionosphere form into long tubes as they orbit the lines.

Brilliant creativity gives us "radio eyes"

Now, through the brilliant and creative use of a radio telescope array in Australia, university undergraduate Cleo Loi - a student at the University of Sydney - has accomplished this feat, and taken it to the next level by producing 3D images of these plasma tubes.

"For over 60 years, scientists believed these structures existed but by imaging them for the first time, we’ve provided visual evidence that they are really there," Loi, who is currently at the Australia Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), said in a press release. "The discovery of the structures is important because they cause unwanted signal distortions that could, as one example, affect our civilian and military satellite-based navigation systems. So we need to understand them."

As Loi explains in the video above, she was able to 3D image these structures by using the Murchison Widefield Array (MWA), a radio telescope located in western Australia in a very novel way. Rather than using the entire array, she split the array down the middle, comparing data from one half to data from the other half - effectively turning the MWA into a large set of radio eyes.

"We saw a striking pattern in the sky where stripes of high-density plasma neatly alternated with stripes of low-density plasma. This pattern drifted slowly and aligned beautifully with the Earth’s magnetic field lines, like aurorae," Loi said, who's work has earned her the 2015 Bok Prize of the Astronomical Society of Australia. "We realised we may be onto something big and things got even better when we invented a new way of using the MWA."

"Too good to be true"?

According to Loi's faculty supervisor at CAASTRO, Dr. Tara Murphy, it wasn't easy for Loi to convince others of what she's found.

"When they first saw the data, many of her senior collaborators thought the results were literally ‘too good to be true’ and that the observation process had somehow corrupted the findings," Murphy said in the CAASTRO press release, "but over the next few months, Cleo managed to convince them that they were both real and scientifically interesting."

"It is to Cleo’s great credit that she not only discovered this but also convinced the rest of the scientific community," Murphy added. "As an undergraduate student with no prior background in this, that is an impressive achievement."

Source: CAASTRO